If you put 4"-6" of space under the existing camper it would give you a lot of room for tanks, etc. The problem is that you couldn't use that space for storage because you couldn't access it unless you accessed it from the floor of the camper. A couple of nice aluminum bins on the sides of the camper, with slide out drawers, would be nice if you didn't have the jacks in the way to limit access to them.
Your cabover part would also be too high for the truck. I think a properly built basement model camper has to be built that way from the initial design. It would give you more "head" room in the cabover part and the cabover part should be longer for a north/south bed.